Submersible electric motors used to drive deep well pumps are usually extremely long relative to their diameter and it has been found necessary to support the rotor shaft of such motors at regular intervals with bearing means. Motors of this type are constructed of a plurality of annular laminations of magnetic material which forms the stator and a plurality of segmented rotor sections connected to the shaft and received in the stator. The bearing means are located between adjacent rotor segments and may comprise sleeve portions surrounding the shaft and connected journals which engage the inner surface of the stator. These journals are preferably stationary with respect to the stator.
An immediate problem which arises with the use of such bearing means is the possibility of rotation of the stationary bearing element due to the effects of the rotating magnetic field produced by the motor stator. Such rotation causes overheating of the bearing which in turn adds substantial heat to the entire motor assembly and results in significant loss of operating efficiency. Additionally, such rotation damages the motor stator and may require premature maintenance or replacement of motor parts.
The problem has been recognized; many attempts have been made to solve the problem. One method is to provide a stator core which is discontinuous in the areas which contact the stationary bearing journal. This is accomplished by including groups of non-magnetic laminations in the motor stator assembly. In this manner, the magnetic field was interrupted at the bearing locations and rotation of the stationary bearing was prevented.
Other attempts to solve the problem have been made by constructing bearings of non-magnetic materials; however, to be successful, such material must also resist the inducement of internal eddy currents. Even these materials have a tendency to rotate in a magnetic field. Thus few materials can satisfy the requirements.